The present invention relates to media for recording, storing and reading magnetic data, and more particularly to means for controlling the surface topographies of magnetic media.
Magnetic disks employ thin films of magnetizable material for storing data in magnetic form. Typically, the magnetic disks are rotatably mounted, with one or more magnetic data transducing heads positioned in close proximity to the recording surfaces of the disks. Each transducing head is movable generally radially relative to its associated disk as the disk is rotated. Rigid magnetic disks are rotated at high speeds during reading and recording operations, to create an air cushion or bearing that supports each transducing head at a controlled distance from its associated recording surface, thus to maintain a consist head glide height or flying height. Also, there are times when the transducing heads contact their associated disks; in particular when the disks are stationary, during disk acceleration from a stop, and during deceleration toward a complete stop.
To increase magnetic data storage density it is desirable to minimize the transducing head flying height. To achieve low flying heights, the recording surface must be flat and smooth, but not so smooth as to cause head media interface stiction. As a result, recording surfaces of magnetic media are intentionally provided with a texture, selected to provide low glide height yet minimize friction and wear.
Traditionally, mechanical abrasion has been used for this purpose. Typically, a cloth, paper or pad coated or saturated with a suitable grit is used. Abrasion removes substantial amounts of substrate material and takes considerable time, adding substantially to media production costs. The abrasion process is low precision, and vulnerable to defect generation.
While mechanical texturing is predominant in commercially available media, chemical etching and printing techniques have been employed to provide texture. More recently, laser energy has been disclosed for media texturing, e.g. as in U.S. Pat. No. 5,108,781 (Ranjan et al.). A pulsed laser beam is focused upon the upper surface of an aluminum nickel-phosphorous substrate to form laser marks, each with a central depression surrounded by a raised rim. As disclosed in application Ser. No. PCTUS95/10697 entitled "PULSED LASER SURFACE TREATMENTS FOR MAGNETIC RECORDING MEDIA", filed Aug. 22, 1995, and assigned to the assignee of this application, laser energy can be used to create outwardly projecting nodules, and to polish a substrate surface. The technique is applied to aluminum Ni--P substrates, and to metallic layers formed on glass substrates.
The continuing trend toward higher data recording densities has lead to the use of alternatives to the traditional aluminum Ni--P substrate, e.g. glass, glass ceramics, and quartz (SiO.sub.2). Although these substrates can be mechanically abrated, the problems discussed above in connection with aluminum Ni--P substrates, particularly low precision and defect generation, are more serious in the case of the non-metallic substrates.
Low melting point materials have been sputtered onto non-wetting substrates to provide texture. For example, gallium has been sputtered onto glass substrates while being maintained above its melting point of 29.8.degree. C. Due to surface tension, the deposited Ga forms spherical liquid features. Subsequent deposition of a magnetic film form alloys and intermetallics that solidify the gallium layer and replicate its topography. An alloy of indium and tin has been applied in a similar manner. Such low melting point materials, however, cannot be applied in a manner that provides separation between adjacent bumps. Further, substrates must be mechanically textured before these materials are sputtered, or the substrate material must have some kind of intrinsic "built-in" texture (such as glass-ceramic substrates discussed immediately below). In connection with glass substrates, several alternative texturing techniques have been attempted, including spin coating, etching, sputtering, and annealing. These have been less than satisfactory in general.
In connection with glass ceramic substrates, mechanical abrasion can cause a "built in" texture in the substrate by removing previously embedded hard particulates. This built in texture is comprised of multiple pits surrounded by "volcanic" rims. Substrates textured in this manner have performed well in CSS testing. However, because of the porosity of metal films deposited onto these substrates, mobile alkali ions (e.g. K.sup.+, Na.sup.+, and Ca.sup.+ ions), particularly adjacent the pits, have been found to migrate from the glass ceramic substrate into the film and ultimately to the exposed surface of the metal films. This problem, known as "hazing" can be diminished by forming the metal film at a highly increased density and by eliminating the pits. However, achieving the built in texture under these circumstances has been difficult, and CSS and stiction performance has not been satisfactory.
Therefore, it is an object of the present invention to provide a more repeatable and reliable method of texturing substrates for magnetic disks utilizing a variety of non-magnetic substrates.
It also is an object to provide a media fabrication process applicable to all types of substrates, that is much simpler and much less costly than conventional texturing and other substrate texturing techniques currently under development.
Another object is to provide a magnetic disk texturing process that is clean room compatible and minimizes the need to handle substrates, to reduce the chances for defects and contamination.
A further object is to provide a magnetic disk having a more uniform texture and fewer defects.
Another object is to provide a substrate texturing process that affords control over the spacing between adjacent bumps or other features, leading to improved CSS performance.
Yet another object is to provide a magnetic disk having a texture that allows lower transducing head flying heights (i.e. one microinch or less), yet enhances CSS performance.